A cermet sintered body, which comprises a hard phase mainly comprising a carbonitride of Ti and a 4a, 5a, 6a Group element component other than Ti (V, Cr, Zr, Nb, Mo, Hf, Ta and W), the hard phase being bound with a binder metallic phase mainly comprising Ni and/or Co is known. Such bodies have excellent plastic deformation resistance, etc. in comparison to super hard alloys which have also been conventionally used. Therefore the sintered bodies are replacing the super hard alloys as cutting tools. The cermet tool is often used in the form in which a hard coating layer of a carbide, a nitride or a carbonitride of Ti or alumina is formed on the surface, to further improve the wear resistance and the plastic deformation resistance.
The formation of a hard layer on the cermet tool described above has been conducted by a gas phase film formation method, such as a physical vapor deposition method, a chemical vapor deposition method, and the like. In this method, however, the hard layer is formed after firing the cermet by conducting another gas phase film forming method as another step. Furthermore, a pretreatment step such as surface polishing, a subsequent surface cleaning or modifying, etc. is necessary before the film formation. As a result, the number of steps is excessive, which leads to an increase in the price of the tool.
An object of the present invention is to provide a cermet tool having a surface coating layer which exhibits a function equivalent to or higher than a hard coating layer of a conventional cermet tool, and being economical in that steps such as a gas phase film forming step is not necessary. Another object of the invention is to provide a process for producing the same.